The subject matter of the present invention is setting compositions of absorbent clay minerals, hydraulic binding agents, fillers and water. They are used principally for producing sealing walls and other such subsurface barriers which are placed in the soil for the purpose of preventing the propagation of pollutants that may have entered the ground.
Pollutants which enter the ground as a result of any kind of uncontrolled events must be prevented from diffusing any further and contaminating the ground water. Such pollutants are, for example, hydrocarbons, chlorinated hydrocarbons, phenols, cyanic and sulfur compounds from gas scrubbing compositions, as well as leachates from leaking refuse dumps.
Measures are already known for preventing the spread into larger areas of such pollutants that may have entered the ground. It is known, for example, to use vertical barrier walls based on foundation engineering technology to enclose soils that have been contaminated with pollutants. The material of such sealing barriers, which are in the form of slit walls or shell walls, are expandable clay minerals, hydraulic cements, water and, in some cases, fillers. After fabrication, compositions containing these materials yield walls which have a greater elasticity than concrete, so that even relatively strong tremors do not tend to cause cracking.
The k values of these walls are approximately 10.sup.-8 ms.sup.-1.
The permeability coefficient k is calculated on the basis of the simplified Darcy equation, EQU k=Q/F.multidot.I cm/sec,
wherein:
Q=rate of seepage in cubic cm per sec PA1 F=filter area in sq cm PA1 .DELTA.h=height of water column in cm PA1 D=thickness of permeated layer in cm PA1 I=hydraulic gradient=.DELTA.h/D
Thus, the permeability is low enough to keep an excavation sufficiently dry; this is not, however, to say that the pollutant concentration outside of the area enclosed by these walls is prevented from exceeding the maximum allowable concentration. A disadvantage of barriers made from these substances is also the fact that the sealing action of clay materials which are contained in these compositions is greatly reduced by chemicals dissolved in water and by organic liquids. The permeability can thus increase by a factor of a thousand as the result of attack by these chemicals (cf. Anderson, Brown, Green, Proc. 8th Am. Res. Symp. USEPA 1982, pp. 179-190).
The problem therefore existed of enveloping pollutants in the soil and of discovering a barrier wall material for the production of confining walls for the envelopment (known as "macroencapsulation") of an area contaminated by a pollutant. Such a material should, after setting, largely prevent the escape of the pollutants from the enveloped area and their penetration into the ground water for a long period of time.